man/sd_bus_message_append_basic.xml

   1 <?xml version='1.0'?> <!--*- Mode: nxml; nxml-child-indent: 2; indent-tabs-mode: nil -*-->
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   6   SPDX-License-Identifier: LGPL-2.1+
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   8   This file is part of systemd.
   9
  10   Copyright 2014 Zbigniew Jędrzejewski-Szmek
  11
  12   systemd is free software; you can redistribute it and/or modify it
  13   under the terms of the GNU Lesser General Public License as published by
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  15   (at your option) any later version.
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  20   Lesser General Public License for more details.
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  25
  26 <refentry id="sd_bus_message_append_basic">
  27
  28   <refentryinfo>
  29     <title>sd_bus_message_append_basic</title>
  30     <productname>systemd</productname>
  31
  32     <authorgroup>
  33       <author>
  34         <contrib>A monkey with a typewriter</contrib>
  35         <firstname>Zbigniew</firstname>
  36         <surname>Jędrzejewski-Szmek</surname>
  37         <email>zbyszek@in.waw.pl</email>
  38       </author>
  39     </authorgroup>
  40   </refentryinfo>
  41
  42   <refmeta>
  43     <refentrytitle>sd_bus_message_append_basic</refentrytitle>
  44     <manvolnum>3</manvolnum>
  45   </refmeta>
  46
  47   <refnamediv>
  48     <refname>sd_bus_message_append_basic</refname>
  49
  50     <refpurpose>Attach a single field to a message</refpurpose>
  51   </refnamediv>
  52
  53   <refsynopsisdiv>
  54     <funcsynopsis>
  55       <funcsynopsisinfo>#include &lt;systemd/sd-bus.h&gt;</funcsynopsisinfo>
  56
  57       <funcprototype>
  58         <funcdef>int sd_bus_message_append_basic</funcdef>
  59         <paramdef>sd_bus_message *<parameter>m</parameter></paramdef>
  60         <paramdef>char <parameter>type</parameter></paramdef>
  61         <paramdef>const void *<parameter>p</parameter></paramdef>
  62       </funcprototype>
  63     </funcsynopsis>
  64   </refsynopsisdiv>
  65
  66   <refsect1>
  67     <title>Description</title>
  68
  69     <para><function>sd_bus_message_append_basic()</function> appends a
  70     single field to the message <parameter>m</parameter>. The
  71     parameter <parameter>type</parameter> determines how the pointer
  72     <parameter>p</parameter> is interpreted.
  73     <parameter>type</parameter> must be one of the basic types as
  74     defined by the <ulink
  75     url="http://dbus.freedesktop.org/doc/dbus-specification.html#basic-types">Basic
  76     Types</ulink> section of the D-Bus specification, and listed in
  77     the table below.
  78     </para>
  79
  80     <table id='format-specifiers'>
  81       <title>Item type specifiers</title>
  82
  83       <tgroup cols='5'>
  84         <colspec colname='specifier' />
  85         <colspec colname='constant' />
  86         <colspec colname='description' />
  87         <colspec colname='size' />
  88         <colspec colname='ctype' />
  89         <thead>
  90           <row>
  91             <entry>Specifier</entry>
  92             <entry>Constant</entry>
  93             <entry>Description</entry>
  94             <entry>Size</entry>
  95             <entry>Expected C Type</entry>
  96           </row>
  97         </thead>
  98         <tbody>
  99           <row>
 100             <entry><literal>y</literal></entry>
 101             <entry><constant>SD_BUS_TYPE_BYTE</constant></entry>
 102             <entry>unsigned integer</entry>
 103             <entry>1 byte</entry>
 104             <entry>uint8_t</entry>
 105           </row>
 106
 107           <row>
 108             <entry><literal>b</literal></entry>
 109             <entry><constant>SD_BUS_TYPE_BOOLEAN</constant></entry>
 110             <entry>boolean</entry>
 111             <entry>4 bytes</entry>
 112             <entry>int</entry>
 113           </row>
 114
 115           <row>
 116             <entry><literal>n</literal></entry>
 117             <entry><constant>SD_BUS_TYPE_INT16</constant></entry>
 118             <entry>signed integer</entry>
 119             <entry>2 bytes</entry>
 120             <entry>int16_t</entry>
 121           </row>
 122
 123           <row>
 124             <entry><literal>q</literal></entry>
 125             <entry><constant>SD_BUS_TYPE_UINT16</constant></entry>
 126             <entry>unsigned integer</entry>
 127             <entry>2 bytes</entry>
 128             <entry>uint16_t</entry>
 129           </row>
 130
 131           <row>
 132             <entry><literal>i</literal></entry>
 133             <entry><constant>SD_BUS_TYPE_INT32</constant></entry>
 134             <entry>signed integer</entry>
 135             <entry>4 bytes</entry>
 136             <entry>int32_t</entry>
 137           </row>
 138
 139           <row>
 140             <entry><literal>u</literal></entry>
 141             <entry><constant>SD_BUS_TYPE_UINT32</constant></entry>
 142             <entry>unsigned integer</entry>
 143             <entry>4 bytes</entry>
 144             <entry>uint32_t</entry>
 145           </row>
 146
 147           <row>
 148             <entry><literal>x</literal></entry>
 149             <entry><constant>SD_BUS_TYPE_INT64</constant></entry>
 150             <entry>signed integer</entry>
 151             <entry>8 bytes</entry>
 152             <entry>int64_t</entry>
 153           </row>
 154
 155           <row>
 156             <entry><literal>t</literal></entry>
 157             <entry><constant>SD_BUS_TYPE_UINT64</constant></entry>
 158             <entry>unsigned integer</entry>
 159             <entry>8 bytes</entry>
 160             <entry>uint64_t</entry>
 161           </row>
 162
 163           <row>
 164             <entry><literal>d</literal></entry>
 165             <entry><constant>SD_BUS_TYPE_DOUBLE</constant></entry>
 166             <entry>floating-point</entry>
 167             <entry>8 bytes</entry>
 168             <entry>double</entry>
 169           </row>
 170
 171           <row>
 172             <entry><literal>s</literal></entry>
 173             <entry><constant>SD_BUS_TYPE_STRING</constant></entry>
 174             <entry>Unicode string</entry>
 175             <entry>variable</entry>
 176             <entry>char[]</entry>
 177           </row>
 178
 179           <row>
 180             <entry><literal>o</literal></entry>
 181             <entry><constant>SD_BUS_TYPE_OBJECT_PATH</constant></entry>
 182             <entry>object path</entry>
 183             <entry>variable</entry>
 184             <entry>char[]</entry>
 185           </row>
 186
 187           <row>
 188             <entry><literal>g</literal></entry>
 189             <entry><constant>SD_BUS_TYPE_SIGNATURE</constant></entry>
 190             <entry>signature</entry>
 191             <entry>variable</entry>
 192             <entry>char[]</entry>
 193           </row>
 194
 195           <row>
 196             <entry><literal>h</literal></entry>
 197             <entry><constant>SD_BUS_TYPE_UNIX_FD</constant></entry>
 198             <entry>UNIX file descriptor</entry>
 199             <entry>4 bytes</entry>
 200             <entry>int</entry>
 201           </row>
 202        </tbody>
 203       </tgroup>
 204     </table>
 205
 206     <para>The value of the parameter is copied into a memory area held
 207     by the message object, stays in the possession of the caller and
 208     may hence be freely changed after this call without affecting the
 209     bus message it has been added to. If <parameter>type</parameter>
 210     is <literal>h</literal> (UNIX file descriptor), the descriptor is
 211     duplicated by this call and the passed descriptor stays in
 212     possession of the caller.</para>
 213
 214     <para>For types <literal>s</literal>, <literal>o</literal>, and
 215     <literal>g</literal>, the parameter <parameter>p</parameter> is
 216     interpreted as a pointer to a <constant>NUL</constant>-terminated
 217     character sequence. As a special case, a <constant>NULL</constant>
 218     pointer is interpreted as an empty string. The string should be
 219     valid Unicode string encoded as UTF-8. In case of the two latter
 220     types, the additional requirements for a D-Bus object path or
 221     type signature should be satisfied. Those requirements should be
 222     verified by the recipient of the message.
 223     </para>
 224   </refsect1>
 225
 226   <refsect1>
 227     <title>Return Value</title>
 228
 229     <para>On success, this call returns 0 or a positive integer. On
 230     failure, it returns a negative errno-style error code.</para>
 231   </refsect1>
 232
 233   <refsect1 id='errors'>
 234     <title>Errors</title>
 235
 236     <para>Returned errors may indicate the following problems:</para>
 237
 238     <variablelist>
 239
 240       <varlistentry>
 241         <term><constant>-EINVAL</constant></term>
 242
 243         <listitem><para>Specified parameter is invalid.
 244         </para></listitem>
 245       </varlistentry>
 246
 247       <varlistentry>
 248         <term><constant>-EPERM</constant></term>
 249
 250         <listitem><para>Message has been sealed.
 251         </para></listitem>
 252       </varlistentry>
 253
 254       <varlistentry>
 255         <term><constant>-ESTALE</constant></term>
 256
 257         <listitem><para>Message is in invalid state.
 258         </para></listitem>
 259       </varlistentry>
 260
 261       <varlistentry>
 262         <term><constant>-ENXIO</constant></term>
 263
 264         <listitem><para>Message cannot be appended to.
 265         </para></listitem>
 266       </varlistentry>
 267
 268       <varlistentry>
 269         <term><constant>-ENOMEM</constant></term>
 270
 271         <listitem><para>Memory allocation failed.</para></listitem>
 272       </varlistentry>
 273     </variablelist>
 274   </refsect1>
 275
 276   <refsect1>
 277     <title>Notes</title>
 278
 279     <para>The <function>sd_bus_append_basic()</function> function
 280     described here is available as a shared library, which can be
 281     compiled and linked to with the
 282     <constant>libelogind</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 283     file.</para>
 284   </refsect1>
 285
 286   <refsect1>
 287     <title>See Also</title>
 288
 289     <para>
 290       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 291       <citerefentry><refentrytitle>sd-bus</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 292       <citerefentry><refentrytitle>sd_bus_message_append</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
 293       <ulink url="http://dbus.freedesktop.org/doc/dbus-specification.html">The D-Bus specification</ulink>
 294     </para>
 295   </refsect1>
 296
 297 </refentry>